1. Technical Field
The present invention belongs to the technical field of semiconductor memory device manufacturing, relates to a method for manufacturing a semiconductor memory device, and more especially, to a method for manufacturing a gate-control diode semiconductor memory device.
2. Description of Related Art
The structure of the mainstream floating gate transistor at present is as shown in FIG. 1, including a drain 102 and a source 103 formed in a substrate 101, and polycrystalline silicon gates 105 and 107 formed on the substrate 101, wherein the electrically-connected polycrystalline silicon gate 107 is called “control gate” and the floating polycrystalline silicon gate 105 is called “floating gate”. The floating gate 105 is isolated with the substrate 101 and the control gate 107 through insulation dielectric layers 104 and 106 respectively. The floating gate technology is first applied to EPROM and EEPROM.
The floating gate transistor, of which the working principle is that the transistor threshold voltage is changed according to the fact of whether there are charges stored or how many charges are stored on the floating gate so as to change the external features of the transistor, has now become the basic device structure of on-volatile semiconductor memories. Currently, with the continuous development of integrated circuits, the size of MOSFET (metal-oxide-semiconductor field-effect transistor) is becoming smaller and smaller, and the transistor density on unit arrays is becoming higher and higher. The leakage current between the source and the drain of the MOSFET is increasing rapidly with the decrease of channel length. All these seriously affect the maintenance of the electrons on the floating gate. With the repeating of erasing and writing, the channel insulation film will be damaged, which may cause the leakage of electrons in the floating gate. Moreover, the minimum sub-threshold swing (SS) of the traditional MOSFET is limited to 60 mv/dec, which restricts the opening and closing speed of the transistor.